The purpose of this work is to investigate various biological and chemical properties of two types of murine cell surface antigens that induce graft rejection: histocompatibility antigens (H-2) and tumor associated transplantation antigens (TATA). In the case of TATAs, the approach is to purify the molecule bearing these antigens from tumor cells and characterize them. Polyclonal and monoclonal antibodies may then be prepared against these molecules and used to investigate their biological properties. Ultimately, suitable DNA probes can be prepared and used to study the genes which encode the molecules. This structural information will lead to an understanding of the mechanism of induction of these antigens and their relationship to the oncogenic process. The structure of these molecules may also provide insights into some of the unique immunogenic properties of tumors, e.g., their ability to escape an apparently strong anti-tumor immune response. In the case of H-2 antigens, the approach is to utilize alloantisera and monoclonal antibodies recognizing class I determinants to examine the molecules expressed on normal and neoplastic cells. Moreover, DNA probes and molecular cloning techniques can be used to study the organization and expression of the genes that encode the molecules. Current specific aims are to identify molecules coded for by the many class I genes present in the mouse genome and to obtain information about the evolutionary history of this polymorphic multigene family.